1. Field of the Invention
The present invention relates to an electrically conductive metal tape for manufacturing electrical contact components, as well as to a plug connector.
2. Description of Related Art
Plug connectors are used in electrotechnical applications. Basically understood, this is a mechanical device made up of a plug and plug socket for opening and closing an electrically conductive connection. Plug contact connections are used in the most varied application areas, for example in motor vehicle electrical equipment, information and communication technology or industrial plant electronics.
A common manufacturing method of such plug connectors is to punch out blanks from a copper or copper alloy tape, and to process these further into plug contacts. Copper has high electrical conductivity. To protect against corrosion and wear, as well as to raise surface hardness, the copper or copper alloy tapes are first tinned. Tin is suitable because of its good corrosion stability, especially as coating material for copper. Besides other coating methods, the application of the coating in a hot-dip method represents a technical standard.
In this connection, the most varied tin alloys are known for surface coating the base material, particularly including tin-silver alloys, since these count among the very good contact materials.
As described in European Patent No. 0 443 291, the base material of one plug contact element is coated with pure tin or a tin-lead alloy, while the other plug contact element has a harder surface coating, applied in a molten procedure, of an alloy containing up to 10% by weight of silver. Besides silver, several further alloying metals are suggested. This approach points the way on manufacturing high quality plug connectors having constant, low contact resistance and least possible force (required) for plugging and unplugging
Another proposal according to German Patent No. 44 43 461 provides that a surface coating applied by a molten method contains a tin alloy, having up to 5% by weight of cobalt. Besides cobalt, the tin alloy can also contain bismuth and indium, as well as a plurality of additional alloying metals.
The known metal tapes, or rather, the plug connectors have proven themselves in practice. However, technical and qualitative requirements of the contact components are rising increasingly with respect to their mechanical and electrical properties. This applies particularly to the use of contact components in difficult or aggressive environmental conditions, for instance, for plug connectors in motor vehicle electrical equipment, and there, above all, in engine electronics. Under such difficult application conditions, requirements can come up, particularly with regard to temperature stability, relaxation stability, corrosion resistance and adhesive strength of the coating, in which the known contact components are pushed to their limit. Peeling-off of the surface coating was observed particularly with components stressed by shearing and being bent.
It is an the object of the invention to create an electrically conductive metal tape for manufacturing electrical contact components, particularly plug contact connectors, having improved adhesive properties between base material and metal coating while guaranteeing temperature stability and surface hardness, good sliding properties and stable contact resistance suitable for the requirements.
This and other objects of the invention are attained by an electrically conductive metal tape for manufacturing electrical contact components, in particular plug connectors, having a base material made of a copper or a copper alloy which has a metal coating, applied by molten technology, made of tin-silver alloy, an intermetallic phase being formed between the base material and the coating, wherein the coating is made of a tin-silver alloy having a silver proportion between 1% and 3.8% by weight. In a preferred embodiment, the invention is a plug connector made from the electrically conductive metal tape.